wound rotor motor vs squirrel cage

What happens in synchronous types of electric motors is a direct application of magnetic field to the rotor windings, which has its own drawbacks and benefits. By short circuiting the rotor winding, this advantage is lost and the motor becomes like a squirrel cage induction motor or SCIM with very low rotor resistance. We have all 3 and I must say wr for that size of motor for us seems to be the least troublesome and least expensive for repair. The general construction of the slots in the rotor is such that the rotor bars are placed close to the surface so as to reduce the reactance. High starting torque without overloading the electrical supply system What is an SCR? In wound or slip rotor slip rings and brushes are used. Induction motors are widely used as industrial drives. They have starting torque ratings about double standard motors and VFDs typically limit the starting current and torque. The rotor of the latter, however, as the name implies, has windings. A Design A motor is a squirrel-cage motor designed to withstand full-voltage starting and to develop locked-rotor torque as shown in MG 1-12.37, pull-up torque as shown in MG 1-12.39, breakdown torque as shown in MG 1-12.38 with locked-rotor current higher than the values shown in MG 1-12.34 for 60 Hz and MG 1-12.25 for 50 Hz and having a slip . The secondary resistors with contactors . It converts electrical energy into mechanical energy and it is used to provide motion. Class B: These motors can be started at a full-load while developing normal starting torque. Some of the advantages, disadvantages and applications of squirrel cage induction motor compared with slip-ring induction motor are discussed below: Fig.1: Wound Rotor Induction Motor. 2) Direct-On-Line For motor rating 2.2kW and below: Low Voltage : 220~240V High Voltage : 380~415V For motor rating 3kW and above: Low Voltage : 380 . #2. Schweitzer Engineering Laboratories 4 Squirrel Cage Example Squirrel Cage Rotor Schematics. Their sole purpose is to allow resistance to be placed in series with the rotor windings while starting (figure below). Autotransformer starting method Star delta starting method Direct-on-line starting method Stator resistance starting method The following four methods are available for starting the slip ring or wound motor. The AC current through these poles will induce a magnetic field in the airgap and the rotor. Note: In Slip ring Induction Motor, Stator is wound for 3 phase winding. The squirrel cage rotor has a simpler design and allows induced current to flow through the copper bars. In slip ring induction motors the rotor is wound type. The windings receive current through some kind of slip-ring arrangement. The conversion process is electro-magnetic induction. Therefore, the external resistance cannot connect with the rotor. Fundamentals of Electrical Drives, Alpha Science International Ltd., 2001. Stator . Cost, Such motors are expensive than other induction motors. HOW DOES A WOUND ROTOR MOTOR WORK? Important differences between squirrel cage and slip ring induction motor: .External resistance: The key difference between the slip ring and squirrel cage motors is that a slip ring motor contains an external resistance which increases rotor resistance and thus, the starting torque in it. The rotor winding of the squirrel cage motor is a short-circuit winding. The benefit of a wound rotor motor is that the resistance of the rotor circuit can be externally varied, to provide either variable resis- tance (in the case of a liquid rheostat) or steps (when a series of external resistors of fixed resistance are used), to maximize the torque to suit a particular application. In squirrel cage rotor, the rotor bars are permanently short-circuited with end rings. In the motor the slip rings, brushes are provided. Disadvantages of Slip ring Induction Motor. It consists of Rotor, Stator and other parts like bearings, cylindrical laminated core, shaft, etc. The wound rotor has the advantage of being able to vary speed by varying the resistance. This method is not applicable to squirrel cage induction motors. "ACIM", which stands for "alternating current induction motor", is an asynchronous type of motor that relies on electric current to turn the rotor. The basic difference between squirrel cage and wound rotor induction motor is as follows; Slip ring Induction Motor : Slip ring motor is complicated in construction due to the presence of slip rings. The wound-rotor motor is particularly effective in applications where using a squirrel-cage motor may result in a starting current that's. Wound-rotor motors deliver speed control of heavy and high . . But rotor can be wound with any number of phases except single phase. Induction motors see use in centrifugal fans and compressors, conveyors, lathe machines, and lifts. Slip rings on a wound rotor AC motor. Three phase motors are classified mainly in two categories based on the rotor winding (Armature coil winding) i.e. Their biggest downside is their lack of speed control, which is why other motors ( wound rotor motors) have been developed to address these applications. . The cut section of a squirrel cage induction motor is shown in Fig.6. High torque with reduced inrush current is one of the main advantages of a wound rotor induction motor (WRIM). Figure 1: A squirrel-cage rotor induction motor. Hence it is called squirrel cage. The rotor of the slip ring motor has a cylindrical core with parallel slots, and each slot consists each bar. Squirrel Cage Induction Motor, Motor, Induction motor, An induction motor rotor can be either wound rotor or a squirrel cage rotor. It has a simple construction. There is wear and tear. 17: Cage induction motors when fed from converters - Application guide. From the appearance, the most obvious difference is that the wound motor has a rotor slip ring, while the Squirrel Cage High Voltage Motor does not. A wound rotor induction motor has a stator like a squirrel cage induction motor, but a rotor with insulated windings brought out via slip rings and brushes. The slot of the squirrel cage motor is not parallel to each other. Figure 1-1 Slip rings rotor or wound rotor [9] The squirrel cage rotor is easier to construct in comparison with the slip rings. Nov 14, 2002. Squirrel cage rotor construction can be stated as follows "Lamination or motor core material are stacked in cylindrical shape, metal bars are placed in to this lamination slots perpendicularly. While the wound rotor allows the user to vary the rotor current during it startup as used in "Motor starter". The stator usually has a standard three-phase winding, and the rotor is made with a field winding. The rotor of the slip ring motor has a cylindrical core with parallel slots, and each slot consists each bar. Construction of rotor: There are two types of rotor construction. The damper winding is an additional winding included on the rotor side. The electric current is generated through electromagnetic induction from the magnetic field of the stator windings. Squirrel cage motors lack in some areas that other styles are better in. For normal running, the resistors are shorted out by shorting the brushes together. The non-salient pole type structure has the following special features, They are of small diameter and of very long axial length to reduce the peripheral velocity. Description. SQUIRREL CAGE INDUCTION MOTOR 1.Constructional feature is very simple. 1. These motors also feature a squirrel-cage or wound design, which has led to the development of motor types such as capacitor start induction run motors, squirrel cage induction motors, and double squirrel cage motors. As the output shaft is connected to the rotor inner component which is looking like a cage. The motor whose rotor is wound type such type of motor is called slip ring induction motor, whereas the squirrel cage motor, has a squirrel cage type rotor. Regular maintenance is required due to the presence of slip rings and brushes. Used to connect the rotor to an external set of resistors Wound rotor types with a step starter, induction with a freq drive and synchronous with a clutch. A conductor is placed in each slot of the rotor. This type of construction offers fewer windage losses. Rotor of a double squirrel cage motor has two independent cages on the same rotor. Wound-rotor motors can be started with low inrush current, by inserting high resistance into the rotor circuit; as the motor accelerates, the resistance can be decreased. Applications of Polyphase Cage Rotor Induction Motors, High speeds are obtained i.e., 1500 to 3000 rpm. The block operates in either generator or motor mode. They also require slip rings and brushes. Low Starting Current, This motor draws less current at start as compared to squirrel cage induction motors. A permanent magnet (PM) motor is an ac motor that uses magnets imbedded into or attached to the surface of the motor's rotor. Method of Starting of Squirrel cage motor & Wound motor Basically the following four methods are widely used for starting the cage motor. NEMA Wound-Rotor Induction Motor: A wound-rotor induction motor is an induction motor in which the secondary circuit consists of a polyphase winding or coils whose terminals are either short-circuited or closed through suitable circuits. These are called wound-rotor induction motors. Cost is high ( 3 times compare to squirrel cage) Large Size. The stator of the induction motor consist of wound poles which can be connected directly to the grid or via a VFD. The figure at left shows the cross sectional diagram of a double squirrel cage rotor. Squirrel cage rotor Wound or slip cage rotor; This rotor is in the form of bars which are shorted at the end with the help of end rings. Difference Between Squirrel Cage and Slip Ring Induction Motor While slip ring induction motors (also known as wound-rotor motor) aren't as popular as squirrel cage induction motors, they do have a few advantages. Inserting resistance to this circuit allows the . Once the rotor reaches final speed, the rotor poles get switched to a short circuit, thus becoming electrically the same as a squirrel cage rotor. Slip ring induction motor is one of the types of 3-phase induction motor and is a wound rotor motor type. Older motors may not stand up to the high voltage spikes generated by the switching devices in the VFD. There are two types of 3-phase induction motors viz. Because the speed variation from no load to full load is very small, the term 'fixed' speed tends to be widely used. Efficiency, 7.Constant speed motor. In squirrel cage rotor no slip rings or brushes. 6.Change in slip is less. Wound rotor induction motors are used in heavy duty drives in the range of hundreds kW, like cement and minerals industries. The rotor of the squirrel cage motor has no winding, and there is no need for the rotor to be electrically connected to any electricity. 1) 1. Squirrel cage rotor: Squirrel cage motor works on the principle of Electromagnetism. Phase wound rotor. It is the most common starting method of synchronous motor.

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